Ohio Sen. Rob Portman’s announcement that he supports same-sex civil marriage has sparked a lot of conversation. I see Portman’s announcement as a missed opportunity for conservatives who share his position. But before turning to why that is the case, it might be helpful to walk through some aspects of the intra-conservative conversation.

One of the more striking aspects of our public policy debates on marriage is that they tend to focus on whether or not state governments or Congress or the Supreme Court ought to authorize same-sex civil marriage (Marriage Equality I, or MEI) rather than whether or not the public sector and civil society organizations ought to do something about the deterioration of marriage among non-college-educated Americans (Marriage Equality II, or MEII).

Many conservatives believe that authorizing same-sex civil marriage will contribute to the larger erosion of marriage, a thesis that has been advanced by Ryan Anderson, Robert George, and Sherif Girgis, among others. Advocates of same-sex civil marriage tend to dismiss this argument by observing that most couples will likely prove indifferent to whether or not same-sex couples are also allowed to have civil marriages, yet this view is entirely compatible with the view that same-sex civil marriage might have an impact on the decision of the marginal couple to marry, as Megan McArdle has observed.

Assuming we accept this possibility — I tend to think that the impact on the marginal marriage candidate will be negligible, but it’s very hard to tell — this impact has to be weighed against the possibility that success in stemming the spread of same-sex marriage will in fact lead to a broader deinstitutionalization of marriage, as a friend of mine suggested last May:

My argument on gay marriage starts from the assumption that the main thing we care about is the indirect effects it will have on far more numerous heterosexual unions, especially those with children. Thus I bracket religious liberty, material benefits to gay couples, symbolic affirmation to all gays, etc. From this perspective, I see the main argument against gay marriage as being that it will change the cultural meaning of marriage to deemphasize procreation and (further) play up the companionate aspect, as well as possible effects of making marriage less attractive to men who see marriage as a way to affirm their masculinity/heterosexuality. Note that men who feel this way are those already least likely to marry.

Countering this, the main argument for gay marriage (in terms of indirect effects on heterosexual unions) is less about it being better for straights than the c. 1990 status quo ante than it being less bad than the counterfactual future where it doesn’t happen. If the right somehow succeeded in defeating gay marriage or, as is more plausible, forestalling it another generation before it happens anyway, the likely outcome is not the c. 1990 status quo ante. Rather, it is almost certain that we would see a push for one of two things. (a) Domestic partnerships which are eventually extended to heterosexuals, or as I think of it “no fault” on steroids. (b) The complete deinstitutionalization of civil marriage. You often see this Solomonic, split-the-baby wisdom coming from libertarians as “why is the state involved in marriage in the first place?” This isn’t even counting the Brad Pitt effect, in which a substantial part of the country would come to see marriage as a discriminatory institution, sort of a family equivalent to the Augusta National Golf Club, and refuse to participate in it.

Basically, you can see marriage almost as a patient where the heterosexual/procreative nature of the institution is a limb that’s developed gangrene which we lack the capacity to treat. You might wish that the gangrene had never set in, but given that it has, your choices are to amputate the limb or watch the patient die. Even if we assume gay marriage is undesirable, it is certainly much less bad to take marriage as it existed c. 1990 and extend it to gays and lesbians than it would be to watch marriage get de-institutionalized entirely or dumbed-down to ephemeral domestic partnerships. The longer we let this fight drag on, the more likely it is that we’ll see a frontal assault on the basic institution. As such, even if one lacks enthusiasm for gay marriage and wish the subject had never been broached, at this point the best thing is to just accept it as less damaging than the fallout from it not happening.

My correspondent’s argument not be a particularly attractive one to opponents of same-sex civil marriage, but I think his logic is compelling.

Given that conservatives are divided on this question — 26 percent of self-identified conservatives support same-sex civil marriage as opposed to 57 percent of moderates and 72 percent of liberals, according to a Pew survey from last fall — I think people on both sides of the issue ought to focus on points of agreement rather than disagreement. Many of those who disagree on Marriage Equality I (should we legalize same-sex civil marriage?) agree on Marriage Equality II (the fact that non-college-educated Americans are far less likely to be in stable marriages than college-educated Americans is a serious social problem that exacerbates unequal life outcomes and merits closer attention). And there is a strong case that when we consider the high level of support for same-sex civil marriage among younger Americans, a focus on Marriage Equality I is making it harder to build a big tent around Marriage Equality II. I made this argument back in October, and I still think it’s sound.

To return to Rob Portman, there is a general perception among liberals that his stance in favor of same-sex civil marriage is an example of what Mark Schmitt has derisively called “Miss America conservatism,” in which conservatives choose issues on which to take a centrist or liberal stance not out of principle, but rather out of personal connection — a family member with mental illness prompts one to back federal funding for mental illness, etc. And this is not an unreasonable view, as Portman didn’t really make an effort to connect his conversion on the issue to the much larger issue of MEII.

Imagine if Portman had said something very different: his son’s experience led him to reflect on the central importance of his own marriage to his life, and to his ability to provide a stable environment for raising children. This led him (a) to think about how we wanted his son to have the same chance but (b) to also think about how millions of Ohio families haven’t had the same chance, as demonstrated by the high and rising share of children raised by single parents, the falling number of married individuals as a share of the adult population, etc. He could talk about how marriage shapes economic outcomes, and how people on both sides of the MEI debate ought to pull together to think hard about the deterioration of marriage.

One possibility is that Portman is using his personal experience as a shield, i.e., the fact that Portman has a gay son might make opponents of same-sex civil marriage less likely to criticize him for changing his stance. By calling for broadening the Marriage Equality conversation to place more emphasize on MEII, he might have attracted more attention than he’d like. But if that’s true, it means that Portman has squandered a valuable opportunity to reframe the marriage equality conversation for fairly short-sighted reasons.